Disrupting the interaction between connexin 43 and calmodulin restores gap junction function and mitigates reperfusion arrhythmias.

In myocardial ischemia-reperfusion (I/R) injury, the downregulation of Cx43 is a critical factor influencing intercellular electrical coupling and the incidence of reperfusion arrhythmias (RA). Restoring Cx43 protein levels in cardiomyocytes has been proposed as an effective strategy to reduce RA. However, the impact of I/R on the functionality of Cx43-based gap junction (GJ) remains unclear. In this study, we utilized a 40-minute hypoxia model that did not alter Cx43 expression in cardiomyocytes but impaired GJ function. This model enabled the assessment of GJ functionality via fluorescent dye transfer without the confounding factor of reduced GJ quantity. Further investigation revealed that hypoxia/reoxygenation (H/R) upregulated calmodulin (CaM) expression and enhanced the interaction between CaM and Cx43. SP15, a peptide mimicking the CaM-binding sequence of Cx43, effectively disrupted the CaM-Cx43 interaction, mitigating H/R-induced GJ dysfunction. Additionally, in an ex vivo rat heart I/R model, SP15 improved myocardial electrophysiological parameters and reduced arrhythmia scores by interfering with CaM-Cx43 binding. These findings provide promising evidence for targeting the CaM-Cx43 interaction to improve GJ function and reduce RA.